The present invention generally relates to circuit board components, and more particularly to processes for assembling and reflow soldering a double-sided circuit component to a pair of opposing substrates.
Various types of circuit board components have been specifically developed for high current and high power applications, such as hybrid and electric vehicles. Such components often comprise a semiconductor device, such as a diode, thyristor, MOSFET (metal oxide semiconductor field effect transistor), IGBT (isolated gate bipolar transistor), resistors, etc., depending on the particular circuit and use desired. Vertical devices are typically formed in a semiconductor (e.g., silicon) die having metallized electrodes on its opposite surfaces, e.g., a MOSFET or IGBT with a drain/collector electrode on one surface and gate and source/emitter electrodes on its opposite surface. The die is mounted on a conductive pad for electrical contact with the drain/collector electrode, with connections to the remaining electrodes on the opposite surface often being made by wire bonding. The pad and wires are electrically connected to a leadframe whose leads project outside a protective housing that is often formed by overmolding the leadframe and die.
Components of the type described above include well-known industry standard package outlines, such as the T0220 and T0247 cases, which are prepackaged integrated circuit (IC) components whose leads are adapted for attachment (e.g., by soldering) to a printed circuit board (PCB). The overmolded housings of these packages protect the die, wire bonds, etc., while typically leaving the lower surface of the conductive pad exposed to provide a thermal and/or electrical path out of the package. Such a path allows the package to be connected to an electrical bus for electrical connection to the PCB, or a heat-sinking mass for dissipating heat from the package. If electrical isolation of the path is necessary, a non-electrically conductive heat-sinking pad is provided between the package and heat-sinking mass. In doing so, the heat-sinking pad increases the thermal resistance of the path, typically on the order of 0.1 to 0.5° C./watt.
A further drawback of packages of the type described above is their size. As an example, in certain high current hybrid vehicle applications, arrays of packages containing MOSFET's in a three-phase configuration are utilized, with two or three devices in parallel per switch. The resulting assembled array may contain, for example, sixteen to twenty-four packages, requiring a relatively large area on the PCB. In high current, high voltage (e.g., 150 to 400 V) hybrid vehicle applications, this situation is exacerbated by the need for paired sets of IGBT's and diodes, with the resulting assembled array twice as many individual packages.
As a solution to the above, commonly-assigned U.S. Pat. No. 6,812,553 to Gerbsch et al. and U.S. patent application Ser. No. 10/707,005 (U.S. Patent Publication 2004/0094828) to Campbell et al. disclose double-sided circuit devices that are packaged between a pair of substrates in such a way as to reduce the overall size of the resulting component while also meeting both current and thermal management requirements. There is a need for assembly processes suitable for mass-producing these and other double-sided circuit components.